Locomotive's Optimum Weight

[pdlethbridge]

Driver size would also have an effect on tractive effort

[WGL]

  Thanks for the explanations, pdlethbridge & Imackattack.  Since our models don't run on steam, can we expect a model of a 2-10-2 to pull more than a model of an 0-6-0, for example?

[lmackattack]

 If the model 2-10-2 weighs more than a 0-6-0 then it should be able to pull better. if they both weigh  the same I would think the 0-6-0 would pull a few more cars due to more axel weight across less drivers.   most model 2-10-2 will weigh more than a 0-6-0 so dont worry LOL 

[WGL]

 Thanks, lmackattack.  I am eagerly looking forward to receiving the DM&IR 2-10-2 next week.  Maybe, I'll have to get a few more ore cars.   

[Yampa Bob]

This is an interesting thread. I have some other thoughts about weight and tractive effort versus actual traction, but I'll reserve comments until later. In the meantime here's a homework assignment for all wannabe engineers:  Define tractive effort in its simplest terms.

[pdlethbridge]

locomotive weight divided by its factor of cohesion.

[HO-Ron]

From Wikipedia:

Tractive effort is the pulling force exerted, by a locomotive or other vehicle. The term is used specifically in railway terminology.

The tractive effort value can be either a theorectical or experimentally obtained value, and will usually be quoted under normal operating conditions. The actual value for a particular locomotive vaaries depending on speed and track conditions, and is influenced by a number of other factors.

When a figure for tractive effort is quoted in technical documentation it is either for the starting tractive effort (at a dead start with the wheels not turning) or as the continuous tractive effort which will be quoted at a particular speed.

[lmackattack]

I agree Yampa this is a great thread with lots of good info.    I rember years ago I spoke with a retired Engineer at the Illinois railway Museum and he said something that alwasy stuck in my head regarding that age old Diesel vs steam pulling power. He said in simple terms a Diesel can start a train that it cant pull and a steam engine can pull a train that it cant start. not sure if you can follow that? but after learning more about trains it makes some sence. but then im biased and think steam still rules!

[pdlethbridge]

 diesel depends on its traction motors. They can overload them at the start but if they  keep it up or they will burn out. Thus they can start more than they can pull. A steam loco, on the other hand, doesn't get to be at full horse power until its above usually 20 mph. Its pulling power increases as it gains speed.

[Steve Magee]

Another often overlooked factor in a locos ability to pull is balance, both on the prototype and the model. For instance, how many times have you heard of a leading or trailing truck spring being removed - or added in some cases - to improve the balance of the locomotive.

There are probably several ways of balancing your steam loco, but the one that is easiest uses two postal scales. With the leading and trailing trucks removed, place the leading set of drivers on one scale and the rear on the other. If the weight on both is about the same it is balanced. If they are dissimilar, either add weight to the end of the loco that is on the lower value, or remove weight - milling etc - from the heavier end. Though I would normally recommend the addition of weight.

I have seen notoriously light pullers dramatically improved when properly balanced. A certain 2-10-2 springs to mind ....

Steve Magee
Newcastle NSW Aust

[Yampa Bob]

Weight distribution is important, however the weight transfer caused by pulling a string of cars also has to be considered.  When pulling a load,  a greater weight is imposed on the rear drivers, a lesser weight is imposed on the front drivers, unless all forces are balanced. The drawbar hitch point location has a direct effect on the trim attitude of the locomotive.

[lmackattack]

thats another good point about the angle of the coupler in relation to the driven wheels. that angel can help or reduce traction for anything that pulls a load behind it.  I compete in sled pulls with a old Mack semi tractor. hitch hight is very important. hight is set by the circut that we pulled in but that hight could change with the diffrent types of suspention the trucks had. We tried to get the frame hight just right so that  hitch hight was in spec thru tech inspection but after a load was chained to the frame it diffred a little. We wanted the wheels spinning as we left the line to get the RPMs up fast then let the truck build its speed before all the weight came up to the front of the sled. This gave us the speed needed shortly out of the gate so that when the weight was at the front of the sled the engine was at its full RPM. The only thing that slowed us down was not having the HP needed to drag all 40,000lbs of dead weight when it was at the front.

heres a vid of the old dog pulling last year at the local fairgrounds
http://www.youtube.com/watch?v=gNigPBpwvQU

[Yampa Bob]

Hey Mack, now we know how you got your nickname. That is a great video, thanks for sharing. Did "Last Call" make a full pull? I'm loading the other one, but it will probably take an hour on my slow dialup.

I love the open class tractor pulls with the multiple Allisons. I attended one and the sound was awesome.

[lmackattack]

Hey Mack, now we know how you got your nickname. That is a great video, thanks for sharing. Did "Last Call" make a full pull? I'm loading the other one, but it will probably take an hour on my slow dialup.

I love the open class tractor pulls with the multiple Allisons. I attended one and the sound was awesome.

Yea I live in the mid west so if it has a motor and wheels you will find a place to hook it to a sled. I have seen a few allisons pull and if they do great. but Im a little old school and like the manual transmissons.

regarding that vid,It pulled short. it went about 282'    300' is a full pull. that truck is a bone stock 1976 Mack with a 237 HP diesel.  the only real mod was the stock fuel pump was turned all the way up. in the other vid we made the year before the truck had a 100% stock fuel settings and only pulled to about 220' but it was on wet ground after a morning rain storm. it had no traction at all